ABSTRACT
An extraction method was designed and scaled up to produce multicomponent polyphenolic extracts from blueberries (Vaccinium corymbosum) of three different varieties. The process was specifically drawn up to comply with green chemistry principles. Extracts were obtained for the direct assessment of their antimicrobial and antiadhesive activities, and their direct use in the control of infections caused by concerning multidrug-resistant nosocomial pathogens. Analytical characterization was performed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Similar qualitative profiles were obtained in the three studied varieties with some significant quantitative differences. Up to 22 different polyphenols were identified with a clear predominance of anthocyani(di)ns followed by flavanols, non-flavonoids, and far behind by flavan-3-ols and procyanidins. The individual content of the main polyphenols was also discussed. A pilot scale extract has been also produced as a proof-of-concept, showing that scaling-up triples the content of bioactive phytochemicals. The effect of the polyphenolic extracts was analyzed against seven multidrug-resistance bacterial species by performing biofilm formation and growth and killing curves assays. All the studied varieties showed antibacterial and antiadhesive activities, being the extract containing the highest concentration of bioactive polyphenols, the most active with a high bactericidal effect.
ABSTRACT
The therapeutic effect of Vaccinium polyphenols against uropathogens has been widely studied. Most attention has focused on the antimicrobial activity against P-fimbriated Escherichia coli strains. The present study investigated the anti-adhesive and anti-biofilm activity of a saline extract of blueberry (Vaccinium corymbosum) targeting intestinal colonization by a highly adherent Klebsiella pneumoniae strain. This strain, responsible for a large outbreak of infection in Spain, was selected on the basis of its remarkable capacity to colonize the gastrointestinal tract of patients. The blueberry extract was obtained using a medium scale ambient temperature system (MSAT) in a novel approach based on the use of an aqueous solvent and addition of mineral salts. The polyphenolic content was determined by liquid chromatography coupled to tandem mass-spectrometry (LC-MS/MS). The findings confirmed that the blueberry extract is a rich source of phenolic compounds, including the most polar polyphenols (mostly non-flavonoids), intermediate polarity compounds (flavan-3-ols and most procyanidins) and low polarity compounds (flavonols and anthocyanins). The extract significantly inhibited biofilm formation and bacterial adhesion to HT-29 colorectal cells by a highly adherent multidrug-resistant K. pneumoniae. Although some individual anthocyanidins (malvidin, delphinidin and cyanidin) and one hydroxycinnamic acid (caffeic acid) proved capable of reducing bacterial adhesion, the unfractionated extract was more active than any of the individual polyphenolic compounds. In addition, the extract displayed considerable potential as an intestinal decolonization treatment in a murine model. The study findings demonstrate the potential value of the V. corymbosum extract as an alternative treatment for K. pneumoniae infections.
